How to tell if a car battery is fully charged

geek84

Hi Folks

I have recently bought my first car. I am not very technical minded, so could someone please answer the following questions-

1. If the car does not start in the morning, say the battery is down, how can I tell that the battery is fully charged, if I try to charge it with cables (jump start) or an auto battery charge starter?

2. If I leave the fan radio, or lights on for a while without turning the engine on, does that drain the battery?

3. How can I tell that the tyres need replacing?


Thanks in advance

molerat

1. You do not charge the battery with jump starters you merely use their power to start and charge the car with its own alternator once going.

2. Yes

3. Tyres have little lumps in the treads which show the minimum tread depth, some have the letters TWI on the sidewall to show where they are. Rub your fingers along the tread and you will feel the indicator.

Wig

You can tell if a battery is flat because when you turn the key:

Car 'A'
A healthy car the engine makes a loud noise and starts after say 2 seconds.

Car 'B'
In a not so healthy car -with a GOOD battery- turn the key, the engine makes a loud -but normal- noise and continues to make the loud noise but does not start, this car has a fuel or ignition problem but has a GOOD battery.

Car 'C'
In an otherwise healthy car which has a FLAT battery, you turn the key the engine makes no noise at all, OR makes a very quiet limping sound and eventually stops making any noise, Or can start off with a slightly loud noise but quickly the noise becomes quieter until nothing, it sounds like it is struggling to make the loud noise that car 'A' makes.


Sorry to explain it in such detail, but I am always amazed when I encounter people who have a car 'B' and they say "maybe it's the battery" :eek:

Anyway, how to tell you have a decent battery, you can try a multimeter on voltage 20 scale and simply measure its voltage but this is not reliable it may say 12.6V and still won't start your car, another battery will say 12.6 and will be a great battery lasting for years.

So you need one of these - but I have not tried one
http://www.machinemart.co.uk/shop/product/details/cvt1-battery-tester

If you have jump started the car with cables, the battery will still be flat, so drive it for at least 10 mins, you won't know if it's good enough until you turn it off and try to start it again.

To "Bump start" a car turn the ignition key to the first click, so the dash lights up, do not touch the key after this, do not turn it as if to start it. Someone in the drivers seat, push down the clutch put it into 2nd gear, keep the clutch down, get your mates to push the car, when your mates cannot go any faster, release the clutch pedal quickly, if it starts give it some accelerator pedal to liven the engine up a bit.

If you are charging your battery, although some chargers indicate theoretical battery condition as good/poor/dead if it says good or poor you won't actually know until you try to start the car, if the charger indicates 'dead' it's likely to be the case. Chargers without indication, you just have to charge overnight and hope for the best when you try to start it.

How to tell if your alternator is working,
use a multimeter to measure volts with the car off 12.5 - 13.5 volts
start car keep meter on the battery watch the voltage reading should rise to 13v - 14.5v
keep meter connected watch the reading and switch on the rear de-mister and headlamps should stay the same 13 - 14.5V
If at any point after starting the voltage drops and stays below what it was when switched off, your alternator is not working properly.

YES,
Leaving the radio on or headlights on will drain a battery, However a good battery will not drain as quickly as poor battery. and some radios are linked to in car displays which use up more power, some radios are very simple with no display and don't use up hardly any power. Leaving lights on is quite a drain at 140 watts 250W if you leave your main beams on.

Tyres
Look in the central part of the tread where the BIG grooves are, at the bottom of the big grooves there are some little bumps in the rubber, these bumps are 1.6mm higher than the rest of the groove. When the surface of the tyre wears down to meet these little bumps your tyres need replacing. i.e the grooves are now 1.6mm deep.

Hammyman

geek84 wrote: »

3. How can I tell that the tyres need replacing?


Thanks in advance

With a tread depth gauge and ideally checked weekly. Cost a couple of quid from motorist shops. Measure 1/3 in from each side and the mid point at two different points on each tyre. Legally needs to be 1.6mm across all readings. I would advise changing the tyre at 2mm as braking efficiency in the wet drops right off below that.

cyclonebri1

Tyres have minimum wear blocks, these run in the grooves and when you are running on these you are illegal.

Batteries?; if a battery is not fully charged after 6 hrs on a standard charger it is kaput. A healthy battery will not need charging unless you do something silly like leaving the sidelights on for a few days, which is becoming ever more unlikely with modern systems.

savemoney

I got one of these plugs in cigarette light

Its telling me mine is in need of charge but not serious. I dont do long journey just Dad taxi and weekly shop usually

http://www.amazon.co.uk/gp/product/B001VC4PVG/ref=oss_product

thescouselander

A good indication of the battery condition can be got from measuring the electrolyte density - you could use a Hydrometer for this and they are much cheaper buying a proper battery tester:


http://www.halfords.com/webapp/wcs/stores/servlet/product_storeId_10001_catalogId_10151_categoryId_165469_productId_530647_langId_-1?cm_mmc=Shopping-_-Google%20Product%20Search-_-Workshop+%26+Tools%2FHand+Tools-_-Halfords+Battery+Hydrometer&source=shopping&istCompanyId=b8708c57-7a02-4cf6-b2c0-dc36b54a327e&istItemId=mptiri&istBid=t


See here for more details


http://www.batterystuff.com/tutorial_battery.html#6

cyclonebri1

But with a healthy battery nothing is needed???;)

OK you might get a few nano secs of warning but an ill battery is just that, plus they don't get better

When you realise your battery is less than 100% it's time for a new one,

Wig

thescouselander wrote: »

A good indication of the battery condition can be got from measuring the electrolyte density - you could use a Hydrometer for this and they are much cheaper buying a proper battery tester:

An hydrometer is a good test, but a lot of batteries are sealed now. and those that aren't sealed the acid barely covers the plates so it's difficult to get your hydrom.. filled up.

forgotmyname

Voltage tester can also be used to check batteries state of charge, 12.8+ is fully charged.

Test after the car has been sitting for at least one hour or overnight. Put the headlights on
for 20 minutes then check again. If it drops below 12.5 start saving/thinking about a new one.

A good overnight charge with a decent charger (12 hours +) May put some life back into it.

epninety

cyclonebri1 wrote: »

But with a healthy battery nothing is needed???;)

OK you might get a few nano secs of warning but an ill battery is just that, plus they don't get better

When you realise your battery is less than 100% it's time for a new one,

The problem is, without further checks, knowing that the battery is the problem. Don't confuse 'State of Charge' with 'State of Health' for a car battery.

A battery thats long due for the scrapheap can easily indicate 100% charge, either on a volts test, or even (less likely) on a load test.

I've got a 55Ah battery here that measures a proper 12.8V when fully charged, but is only capable of delivering about 10Ah before it's dead - that one is scrap.

The battery on one of my cars typically measures well below 12V in the morning - there's nothing wrong with it, it just never gets fully charged because there is (or rather was until yesterday) a charging system fault. It's been like that for months, but I've not had chance to fix it. There's nothing wrong with that battery (though it's service life will have been shortened by the abuse).

Using one of the cheap plugin gauges doesn't really tell the whole story, only hints. It would have indicated my battery was charging (which it was) but not that it was only charging very slowly. It could have lead me to spend a packet on a new battery, when the issue was elsewhere.